Patent attributes
An object of the invention is to diagnose a failure of an addition valve provided in the exhaust system of an internal combustion engine. To achieve the object, post injection through a fuel injection valve of the internal combustion engine and reducing agent addition through the reducing agent addition valve are performed at different timings, the quantity of fuel injected through the fuel injection valve when the post injection is performed and the quantity of reducing agent added through the reducing agent addition valve when the reducing agent addition is performed are estimated based on a same parameter, and it is diagnosed that the reducing agent addition valve has a failure on condition that the difference between the estimated fuel quantity and the estimated reducing agent quantity exceeds a predetermined quantity.
